Unprofessional soldering practices are the nightmare of ANY electronics manufacturer or service shop. 

GOOD soldering is essential to the performance of your project. A "cold" solder connection is caused by too little heat OR by heating only the component wire and not the wire and PC copper foil together. 

The tell-tale sign of too little heat is a dull, rough-looking connection. If you heat only the wire, the solder forms a cute ball around the wire, and rosin may completely insulate your ball from the copper.